FICO losing its monopoly isn't the best reason to sell the stock -- so here's a better reason.Raise your hand if you know what a FICO score is. Now, keep your hand raised if you know the company that developed the FICO score is also a publicly traded stock: Fair Isaac (FICO -9.08%).I'm seeing a lot of hands up right now, from investors who own Fair Isaac stock today -- and kind of wish they didn't. What just happened to FICO?Shares of Fair Isaac plummeted 16% through 2:10 p.m. Tuesday, and all because of on ...